Mobile IP enables a mobile node to move freely from one point of connection to another. During the movement of the mobile node from one connection point to another there should be no disruption of the TCP end-to-end connectivity. In order to extend Mobile IP for use by cellular telephone companies and check the mobile node's identity, an authentication, authorization, and accounting (“AAA”) mechanism may be used. AAA may be used to provide the authentication of a mobile node (“MN”) when mobile node is connected to the point of the agent on the foreign domain (foreign agent).
Authentication in 3GPP and GSM is typically done by first asking the identity of the mobile node to the network. The mobile node sends an attach request to the foreign domain's MSC or SGSN or 3GSGSN. The 3GSGSN asks the identity of the mobile node to the home authentication server (the HLR). When the identity is verified, the SGSN asks for authentication quintuplets or triplets in GSM. When the SGSN receives the quintuplets or triplets it sends an authentication request to the mobile node. The mobile node uses its local algorithms to sign the random number received in the quintuplet from the SGSN. The mobile node may then verify the network identity when in 3GPP and send back a signature to the visited SGSN. The foreign SGSN verifies the signature by comparing it to the expected result received in the quintuplet. When this matches, then the three entities (the mobile node, the foreign authentication server and the home authentication server) are authenticated and trust each other.
This authentication process, however, requires many steps and communications from the foreign domain to the home domain. Not only is this time consuming, but the communications may be costly.